Conventionally, information on the motion of the object is regarded as important when the object is extracted from a motion picture that is captured by a camera in the vehicle or the like.
More practically, a method that calculates motion vectors for a unit of pixel blocks (e.g., a pixel block having 16×16 pixels), or a method that highly accurately detects the motion for every pixel has been used for image recognition. Those methods are disclosed in Japanese patent documents JP-A-H07-302328, and JP-A-2003-288600, for example.
When the motion information is calculated for a unit of pixel blocks, the extraction of pedestrian motion is difficult due to the smallness of the pedestrian image in the screen. That is, if the position of the pedestrian is relatively far and that makes the size of the pedestrian substantially same as or smaller than the size of the pixel block, the pedestrian image is small and motion vectors cannot be generated from the image of the pedestrian who is walking at a normal speed. As a result, the extraction of the pedestrian motion based on those motion vectors is difficult.
On the other hand, when the motion information is calculated for every pixel, a couple of problems are encountered, such as a signal-noise distinction problem due to the pseudo-motion of stationary objects caused by the camera movement and/or uneven brightness, or a calculation load problem that the detection of the pedestrian requires an huge amount of calculation. Further, maintaining consistency throughout the pixel-by-pixel processing of the detection method and the pixel block processing of the widely-used MPEG format may sometimes be difficult.